The relays in earlier design boards are soldered on and cannot be replaced. Later design boards fea- ture replaceable
FBRA18 rethermalizers use interface board
1J2
1
K1 |
| K2 |
HEAT |
| WATER |
|
|
|
K3
BLOWER
J3
POWER
J1 | CYCLE WATER BLOWER |
INTERFACE BOARD P/N
On interface board
TEMPERATURE PROBE
A temperature probe is located on the front centerline of the cookpot. The probe is a type of thermo- stat in which the resistance varies directly with the temperature. That is, as the temperature changes, so does resistance, at a rate of approximately 2 ohms for every 1° of rise or fall. Circuitry in the controller monitors the probe resistance and controls burner firing when the resistance exceeds or falls below a programmed temperature (setpoint). The temperature is programmed by means of up or down arrow buttons on the face of the controller.
WATER LEVEL SENSORS (FBRA18 Only)
A pair of water level sensors is arranged one above the other on the left front of the FBRA18 cook- pot. When water contacts the sensors they are grounded. The lower sensor acts as a safety device to keep the burner from firing when there is no water in the cookpot. When the sensor is grounded by contact with water, a transistor on the interface board is biased and the heat relay (K1) pulls in, sup- plying power to the blower via relay K3 and to the gas valve via the ignition modules. Grounding the upper water level sensor causes the water relay (K2) to open. This cuts power to the water sole- noid valve, which closes, cutting off water flow into the cookpot.